v0.3.0: data size reductions via SH clustering

See "Making Gaussian Splats more smaller" blog post for details/images. Largest change is that at low quality levels, spherical harmonics data now does vector quantization / clustering for large space savings.

• Change: asset format has changed, you will have to re-create the gaussian splat assets.
• Size: "Very High" quality level is now ~2x smaller than gaussian splat PLY file (was larger than PLY file previously), at virtually no quality loss.
• Size: "Low" quality level is now smaller than before (12.2x -> 14.9x size reduction), and slightly better quality.
• Size: "Very Low" quality level is not complete garbage now. Size about the same (18x reduction), but quality PSNR increased from ~24 to ~32.
• UX: asset creation window now displays data sizes for individual components (position, color, SH etc.)

v0.2.0: splat asset, faster sort, smaller data

See "Making Gaussian Splats smaller" blog post for details/images.

• Change: no longer reads the splat .ply file directly, rather use "create gaussian splat asset" wizard to create the asset.
• Feature: splat asset creation can now pick various options between file size & fidelity. Up to 10x smaller data sizes still look okay.
• Feature: splat rendering now respects the depth buffer, i.e. regular 3D unity objects can be "in the scene".
• Feature: splat rendering now respects object transform, can tilt/mirror the splat object to better align with usual orientation.
• Perf: use AMD FidelityFX based sorting on suitable platforms (DX12, Metal, Vulkan), which is several times faster than previous sorting routine.
• Perf: some optimizations to make rendering faster, esp. on Mac. This is still a regular "render splats like particles" renderer though.
• UX: splats now render without entering play mode.
• UX: source splat directory picker has dropdown for 10 previously used locations.
• Debug: various splat rendering modes (render as points, etc.)

v0.1.0: initial toy

Initial toy! See blog post.